Map data for electronic navigation devices, such as GPS based personal navigation devices like the GO™ from TomTom International BV, comes from specialist map vendors such as Tele Atlas Nev. Such devices are also referred to as Portable Navigation Devices (PND's). This map data is specially designed to be used by route guidance algorithms, typically using location data from the GPS system. For example, roads can be described as lines—i.e. vectors (e.g. start point, end point, direction for a road, with an entire road being made up of many hundreds of such segments, each uniquely defined by start point/end point direction parameters). A map is then a set of such road segments, data associated with each segment (speed limit; travel direction, etc.) plus points of interest (POI's), plus road names, plus other geographic features like park boundaries, river boundaries, etc., all of which are defined in terms of vectors. All map features (e.g. road segments, POI's etc.) are typically defined in a co-ordinate system that corresponds with or relates to the GPS co-ordinate system, enabling a device's position as determined through a GPS system to be located onto the relevant road shown in a map and for an optimal route to be planned to a destination.
To construct this map database, Tele Atlas utilises basic road information from various sources, such as the Ordnance Survey for roads in England. It also includes, but is not limited to, the deployment of a large, dedicated team of vehicles driving on roads, plus personnel checking other maps and aerial photographs, to update and check its data. This data constitutes the core of the Tele Atlas map database. This map database is being continuously enhanced with geo-referenced data. It is then checked and published multiple times a year to device manufacturers like TomTom.
GPS navigation systems are also know for use by pedestrians. Indeed, it is possible to use personal navigation devices such as the TomTom™ GO™ whilst a pedestrian as well as within or on a vehicle. However, the map data provided by vendors such as Tele Atlas may not contain as much detail as is desirable in order to provide directions, especially for pedestrians. Thus, it is desirable to be able to increase the information content of such map data.